Simon is the co-creator, along with Jack "King" Kirby, of Captain America (read that: Stan Lee can't mooch credit for it. Seriously. In the recent solicitation for Stan Lee's Mighty 7 comic, it describes him as "the creator of Spider-Man and the X-Men." Then again, Lee might reel it in with him, since it was Simon who first hired him and got him into comics). But Simon did a lot more than that. Along with Kirby, he created the Boy Commandos, the Newsboy Legion, Manhunter, and a shitload of romance comics. A little less noteworthy to others was his alignment with the counterculture movement of the 60's that gave us Prez (I have a complete run) and Brother Power, The Geek (I'm sorry, but the missile-making hippies always makes me laugh).
The bright side, such as it is, is that, unlike Martin Nodell, he lived long enough to see his creation made into a movie. A great movie, not counting the Albert Pyun misfire from the 90's (I'm not mentioning the TV movies because I remember totally loving them when I was a kid).
Rest well, Simon. You have inspired millions, and have earned your reward.